The majority of plants obtain most or all of their nitrogen requirements from the soil. The adequate provision of nutrient nitrogen in soil for plant growth is one of the foremost agronomic problems. The nitrogen in the soil is found to occur primarily in three forms: organic nitrogen, ammonium nitrogen and nitrate nitrogen, of which ammonium nitrogen and nitrate nitrogen are the primary forms utilized by plants. This nitrogen is absorbed by plants in solution from the soil in the form of ammonium ions and nitrate ions.
The ammonium nitrogen in the soil occurs principally as colloidal-bound nitrogen, only very small quantities of the ammonium form of soil nitrogen are lost from the feeding zone of the plants by leaching.
The nitrate nitrogen in the soil is derived from the oxidation or nitrification of ammonium nitrogen by soil bacteria or by the addition of inorganic nitrate fertilizers such as ammonium nitrate, sodium nitrate, potassium nitrate and calcium nitrate. The inorganic nitrate compounds are readily soluble in water and the aqueous soil medium. When so dissolved, the nitrate nitrogen largely exists as the nitrate ion.
The nitrogen contained in the nitrate, in contrast to ammonium nitrogen, is not adsorbed by the sorption carriers of the soil. A further discussion of the nature of this nitrogen problem in agriculture is set forth in U.S. Pat. No. 3,135,594.
Because of the anionic nature of this nitrate ion, nitrate nitrogen is rapidly leached by rainfall and irrigation and readily lost from the feeding zone of the plants. Further, the nitrate nitrogen is reduced by many soil bacteria to nitrogen gas. The latter process is known as denitrification and accounts for an additional loss of large quantities of nitrate nitrogen from the soil. The yearly loss from leaching and denitrification amounts to from 20 to 80 percent of the nitrate nitrogen found in the soil.
To overcome the loss of ammonium nitrogen in the soil by nitrification, it is the practice to add to the soil a nitrification inhibitor.
Representative nitrification inhibitors and their use can be found in U.S. Pat. Nos. 3,135,594, 3,494,757 and 3,635,690 and British Pat. No. 1,592,516.
While the known inhibitors are effective in reducing nitrification, they, for the most part, have a major drawback in that they must be incorporated into the soil within a very short period of time, i.e., a few minutes to a few hours in order to avoid losses of the inhibitor to the air. This requirement for quick incorporation hinders and/or restricts the use of nitrification inhibitors in agronomic practices where no till or minimum till is employed and in those areas where fertilizers are added and incorporation is delayed.